The present invention relates generally to electronic article surveillance (EAS) systems and more particularly to a novel EAS marker for use in an EAS system and to a method of manufacturing said EAS marker.
The problem of protecting articles of merchandise and the like against theft has been the subject of numerous technical approaches. One such type of approach has been to attach to the article an electronic tag or marker that is adapted to trigger an alarm or the like if the article of merchandise is moved beyond a predetermined location and the electronic marker has not been deactivated or removed from the article of merchandise. In the aforementioned type of approach, a transmitting apparatus and a receiving apparatus are typically situated on opposite sides of a passageway leading to an exit of the premises being protected, the transmitting apparatus and the receiving apparatus together defining an interrogation zone. The transmitting apparatus is typically used to transmit over the interrogation zone an interrogation signal that is recognizable by the EAS marker and that causes the EAS marker, if activated, to emit a response signal. The receiving apparatus is typically used to detect the presence of a response signal from an activated EAS marker located within the interrogation zone. The detection by the receiving apparatus of a response signal indicates that the EAS marker has not been removed or deactivated and that the article bearing the marker may not have been paid for or properly checked out. Typically, the detection of such a response signal by the receiving apparatus triggers an alarm.
Several different types of EAS markers have been disclosed in the literature and are in use. In one type of EAS marker, the functional portion of the marker consists of either an antenna and diode or an antenna and capacitors forming a resonant circuit. When placed in an electromagnetic interrogation zone created by the transmitting apparatus, the antenna-diode marker generates harmonics of the interrogation frequency in a receiving antenna in the receiving apparatus; the resonant circuit marker causes an increase in absorption of the transmitted signal so as to reduce the signal in the receiving apparatus. The detection of the harmonic or signal level change indicates the presence of the marker in the interrogation zone. With this type of system, the marker is not amenable to deactivation and, therefore, must be removed from the article of merchandise at the time of purchase so as not to trigger the alarm when the merchandise is removed from the store.
Another type of EAS marker includes a magnetostrictive element, also referred to in the art as "a resonator." Typically, the resonator is in the form of a ribbon-shaped length of an amorphous magnetostrictive ferromagnetic material. Said type of EAS marker also typically includes a biasing magnetic element. The resonator is fabricated such that it is mechanically resonant at a predetermined frequency when the biasing element has been magnetized to a certain level and the resonator is brought into an interrogation zone consisting of an AC magnetic field of the predetermined frequency. In use, the biasing element is activated, i.e., magnetized, and the marker is brought into the interrogation zone, thereby causing the resonator to mechanically resonate at the predetermined frequency. This resonant signal radiated by the resonator is then detected by circuitry provided in the receiving apparatus. By demagnetizing the biasing element, the bias is removed from the resonator; accordingly, when subjected to the AC magnetic field, the resonator no longer resonates to produce a detectable magnetic field. The marker can thus be activated and deactivated by magnetizing and demagnetizing the biasing element.
Examples of the aforementioned magnetomechanical type of EAS marker are disclosed in the following U.S. patents, all of which are incorporated herein by reference: U.S. Pat. No. 4,510,489, inventors Anderson, III et al., which issued Apr. 9, 1985; U.S. Pat. No. 4,510,490, inventors Anderson, III et al., which issued Apr. 9, 1985; U.S. Pat. No. 4,622,543, inventors Anderson, III et al., which issued Nov. 11, 1986; U.S. Pat. No. 5,351,033, inventors Liu et al., which issued Sep. 27, 1994; U.S. Pat. No. 5,469,140, inventors Liu et al., which issued Nov. 21, 1995; U. S. Pat. No. 5,495,230, inventor Lian, which issued Feb. 27, 1996; U.S. Pat. No. 5,568,125, inventor Liu, which issued Oct. 22, 1996; and U.S. Pat. No. 5,676,767, inventors Liu et al., which issued Oct. 14, 1997.
U.S. Pat. No. 4,510,489, which is illustrative of the aforementioned magnetomechanical type of EAS marker, discloses an elongated ductile strip of magnetostrictive, ferromagnetic material adapted, when armed, to resonate mechanically at a frequency within the range of an incident magnetic field. Suitable amorphous ferromagnetic metals, or metallic glasses, are disclosed for example in U.S. Pat. No. 4,553,136. Exemplary materials include the METGLAS alloys. Said strip is disposed adjacent to a ferromagnetic element, such as a biasing magnet capable of applying a dc field to the strip. The biasing magnet has a configuration and disposition adapted to provide the strip with a single pair of magnetic poles, each of the poles being at opposite extremes of the long dimension of the strip. The composite assembly is placed within the hollow recess of a rigid container composed of polymeric material such as polyethylene or the like, to protect the assembly against mechanical damping. The biasing magnet is typically a flat strip of high coercivity material such as SAE 1095 steel, Vicalloy, Remalloy or Arnokrome. Said biasing magnet is held in the assembly in a parallel, adjacent plane, such that the high coercivity material does not cause mechanical interference with the vibration of the strip. Generally, said biasing magnet acts as one surface of the package. Alternatively, two pieces of high magnetic coercivity material may be placed at either end of the strip, with their magnetic poles so arranged as to induce a single pole-pair therein. Alternatively, the bias field can be supplied by an external field coil pair disposed remotely from the marker in the exit passageway.
A magnetomechanical EAS marker that is integrated with an article of merchandise is disclosed in U.S. Pat. No. 5,499,015, inventors Winkler et al., which issued Mar. 12, 1996, and which is incorporated herein by reference. According to the aforementioned patent, the article of merchandise is provided with a structural member having an integrally formed cavity. A magnetostrictive element is housed within the cavity, the cavity being sized and shaped to house the magnetostrictive element without constraining the mechanical resonance of the magnetostrictive element. The cavity is closed by a sealing member affixed on the outer surface of the wall in a position such that the sealing member overlies the opening of the cavity. A biasing element is mounted on the outer surface of the sealing member, the biasing element being magnetically biased to cause the magnetostrictive element to be mechanically resonant when exposed to an alternating electromagnetic field generated at a selected frequency by the EAS system. According to an alternative embodiment, the biasing element may be formed as a layer of magnetic ink printed on the outer surface of the sealing member.
A self-biasing magnetostrictive element for a magnetomechanical EAS system is disclosed in U.S. Pat. No. 5,565,849, inventors Ho et al., which issued Oct. 15, 1996, and which is incorporated herein by reference. According to the aforementioned patent, the self-biasing magnetostrictive element is formed by first annealing a ribbon of ferromagnetic material in the presence of a magnetic field applied in a transverse direction relative to the longitudinal axis of the ribbon, and then annealing the ribbon a second time in the presence of a magnetic field applied in the direction of the longitudinal axis. The twice-annealed ribbon exhibits remanent magnetization along the longitudinal axis and has plural magnetic domains situated along the longitudinal axis. Said self-biasing magnetostrictive ferromagnetic element may be contained within a cavity of a plastic housing to form an EAS marker.
In U.S. Pat. No. 5,494,550, inventor Benge, which issued Feb. 27, 1996, and which is incorporated herein by reference, there is disclosed an EAS tag and a method of making the same. The method of the aforementioned patent comprises providing a continuous web of electrically insulative material, applying to opposed surfaces of the electrically insulative material web a succession of first and second electrically conductive coils and applying to the succession of first electrically conductive coils a normally electrically insulative deactivation structure extending across the first coil succession and convertible to be electrically conductive, the improvement comprising the step of providing an electrostatic charge drain in electrically conductive relation with each of the first electrically conductive coils substantially throughout the manufacture of the tags. The new step may be practiced by providing an electrically grounded, elongate, electrically conductive member across the succession of first electrically conductive coils in electrical continuity therewith.
In U.S. Pat. No. 5,357,240, inventors Sanford et al., which issued Oct. 18, 1994, and which is incorporated herein by reference, there is disclosed an EAS tag with a mechanically vibrating magnetic element and an improved housing and a method of making the same. The EAS tag of the aforementioned patent comprises a tag body having a central region, side wall regions connected to and integral with the central region and flap regions connected to and integral with the side wall regions. The tag body has fold lines at the junctions of the central and side wall regions and at the junctions of the side wall regions and the flap regions. By folding the tag body along these fold lines and, in the course of the folding procedure, inserting a first magnetic element, a substantially closed box-like housing with the first magnetic element loosely housed therein is formed.
Still another type of magnetomechanical EAS marker, which type is also one of the most widely used types of magnetomechanical EAS markers, comprises a plastic sheet material (e.g., styrene) which carries a heat seal coating. Said plastic sheet material is subjected to a thermoforming process to form a rectangular box-like housing with an open top bordered by a surrounding flange. A resonator is inserted into the housing through the open top, the resonator being curved slightly downwardly about its longitudinal axis. A clear, flexible, plastic sheet (e.g., polyethylene), often referred to as "lidstock," is placed over the top of the housing and is heat-sealed or laminated to the border flange so as to close the housing, thereby encasing the resonator therewithin. Due to the aforementioned process of laminating the lidstock to the housing, a downward curve or "pillow" is typically formed in the midsection of the lidstock, said pillow delimiting upward movement of the resonator within the housing. A double-sided adhesively-coated carrier sheet is laid down over the lidstock and is secured to the border flange of the housing. A biasing magnetic element is secured to the underside of the carrier sheet. A peelable liner is applied to the top surface of the carrier sheet. When using the marker, the liner is peeled from the carrier and the exposed adhesive surface thereof is pressed against a desired article of merchandise, thereby securing the article and the marker together. Typically, the marker is manufactured as part of a batch using a multi-stationed, turntable-containing apparatus analogous to that described in U.S. Pat. No. 5,357,240. A commercial embodiment of the aforementioned marker is sold by Sensormatic Electronics Corporation (Deerfield Beach, Fla.) under the "UltraMax" trademark.
Although the aforementioned type of marker has been successful, the marker does possess some limitations. For example, as pointed out in U.S. Pat. No. 5,357,240, the flange of the housing, although needed for mounting the lidstock, increases the size of the housing, and for many applications, is aesthetically unattractive. Consequently, this prevents use of the marker with certain types of articles, and hence, in certain markets. In addition, the procedures carried out in fabricating the marker can result in the undesired bonding of the resonator between the lidstock and the marker housing. If this occurs, the required mechanical vibration of the resonator may be restricted and the resulting marker may not perform acceptably. Furthermore, the heat seal coating on the housing flange remains soft even after the marker manufacture has been completed. As a result, during shipment of the marker, the resonator may become attached to or lodged against the heat seal coating of the housing or may become stuck between the lidstock and the housing, thereby impeding the desired resonance of the resonator. Moreover, even if the resonator does not become lodged between the lidstock and the flange during manufacture or shipment of the marker, the mechanical vibrations of the resonator during use and/or the magnetic attraction between the resonator and the biasing element may cause the resonator to become lodged between the lidstock and the flange, thereby impairing performance.
Still another limitation of the aforementioned marker is that the marker is not highly resistant to being crushed by downward pressure applied from the top of the marker. Still yet another limitation associated with the aforementioned marker is that the above-described batch-wise technique for manufacturing the marker is not optimal in terms of throughput.